Repeated exposure to cocaine produces enduring behavioral changes, such as the sensitization of the motor stimulation. This proposal seeks to identify the cellular basis for the enduring behavioral plasticity produced by withdrawalfrom repeated cocaine administration. The focus of this work is on neuroadaptations in the glutamatergic projection from the prefrontal cortex to the nucleus accumbens. Accordingly, the project is comprised to two specific aims, one describing experiments to evaluate presynaptic changes in glutamate release in the nucleus accumbens, and another aim is designed to characterize postsynaptic changes. The projects involve in vivo estimates of extracellular glutamate and subcellular localization of specific proteins shown during the present grant period to be involved in cocaine addiction, including Homer, Lim kinase, F- actin, cystine-glutamate exchanger, as well as certain surface receptors whose trafficking is altered by cocaine, including ionotropic glutamate and adenosinel receptors. The importance of alterations in these proteins will be evaluated not only by examining for influences of these proteins on enduring changes produced by repeated cocaine in extracellular glutamate, but also on the capacity of withdrawalfrom repeated cocaine to induce locomotor sensitization. In order to accomplish this, it will often be necessary to design novel reagents to affect intracellular protein levels and/or function. For example, adeno-associated virus to transfect neurons with various Homer cDNA's or Tat-HIV fusion proteins to inhibit Lim-kinase have been constructed. The primary significance of this research is two-fold. First, novel neuroadaptations associated with withdrawal from repeated cocaine administration will be demonstrated, and second, novel reagents to normalize these adaptations and alter the development or expression of cocaine-induced behavioral plasticity will be characterized.